Performance-Based Navigation (PBN), including the widely used Required Navigation Performance (RNP) and Area Navigation (RNAV) instrument procedures, is a key part of airspace modernization worldwide. For example, RNAV and RNP-based procedure deployment is a component of the United States' airspace modernization, the Federal Aviation Administration (FAA) NextGen program, that is implementing new PBN routes and procedures to leverage emerging technologies and aircraft navigation capabilities. Modern commercial aircraft fly PBN flight paths with very high precision. The aircraft can exploit high accuracy provided by global positioning system (GPS)-based navigation systems, modern Flight Management Systems (FMSs) and Flight Control Systems (FCSs). Due to this highly accurate path-keeping capability, the use of PBN removes much of the variability traditionally seen in aircraft flight paths, and results in highly repeatable operations.
The benefits of using RNAV and RNP procedures thus include improved aircraft stability on approach, improved aircraft predictability for air traffic control, reduced fuel burn, lower track miles, improved airport capacity and paths tailored to avoid noise sensitive areas. However, these same procedures can be detrimental for the same reason because increased precision on flight paths can also concentrate noise over underlying communities.
While accuracy and repeatability can be desirable, there are a number of operational and safety issues that could benefit from judicious variation in flight paths. For example, in approach operations, a concentrated noise footprint stemming from repeatable operations creates noise issues for communities under the flight paths. In addition, fixed, consistent flight paths mean that air traffic controllers (ATC) lose some ability to fine-tune aircraft longitudinal spacing that the ATC once exercised by vectoring traffic. Furthermore, highly repeatable path-keeping traffic means a higher risk of loss of separation between aircraft if the concentrated portions of the traffic streams conflict.
Existing solutions related to path variation with use of RNP are limited to offsetting flight paths relative to the originally-defined procedure. For example, ATC may pull some traffic off of fixed routes to avoid or organize traffic using vectors. However, this negates efficiency and other benefits of fixed track use, and limits the ability of on-board aircraft systems to provide alerts supporting high integrity guidance and navigation. Further solutions provide for aircraft to fly an offset path, in which both the offset path and associated boundaries are shifted by an amount of the offset. However, this method is not usable in constrained airspace associated with arrival, approach and departure routes in a vicinity of airports where locations of original boundaries may be integral to safe operations.
What is needed is a method that enables use of the full margins of an RNP procedure based on measured performance to support air traffic controllers with more effective tools for determining clearances that will retain efficiency while managing the spacing/timing of aircraft and also addressing community noise concerns and constraints.